1. Field of the Invention
The present invention relates to a shuttle valve for a reciprocating pneumatic motor for hydraulics, and more particularly to such a shuttle valve which has a press rod supported on a compression spring in it that causes the pneumatic piston to change its stroke subject to the condition of the load.
2. Description of the Prior Art
U.S. Pat. No. 5,341,723 which is issued to the present inventor discloses a reciprocating pneumatic motor for hydraulics which has a pair of guide grooves on the inner wall of a cylinder provided, together with a pneumatic piston and a shuttle valve to function pneumatically. The piston has a seal ring which passes the guide grooves to allow air to flow into the shuttle compression chamber, pushing the shuttle valve and opening up a channel for the venting of air. The piston is integrated with a ring plate using plastic ultrasound technology which simplifies the structure of the pneumatic motor. This structure of reciprocating pneumatic motor is functional. However, because the stroke of the pneumatic piston maintains unchanged when bearing no load, the working efficiency of the reciprocating pneumatic motor is slightly low.